The present invention relates to construction engineering and has particular reference to reversible, percussive devices for ground perforation.
The invention can be used with particular advantage for perforating the ground by compaction thereof. It may also be advantageous to employ this invention in driving pipes into the ground, for example, when laying underground piping without trench excavation.
Ground perforating devices powered by a gaseous medium, for example air, under pressure are known in the art. These devices are mostly reversible, i.e. they can move forward to advance into the ground and can also move in reverse, out of the ground.
A known ground perforating device has a cylindrical body with a pointed front end. The cylindrical body accommodates a hammer adapted to reciprocate therein. The rear portion of the hammer has a hollow which accommodates a stepped sleeve secure in the cylindrical body by means of a screwed joint. The sleeve has two positions: one for forward movement and the other for reverse movement of the ground perforating device. Attached to the rear end of the sleeve is a hose for supplying a gaseous medium, for example, compressed air. The space between the outer surface of the hammer and the inner surface of the cylindrical body forms a front power chamber. The space in the rear end of the hammer between the interior surfaces thereof and the sleeve forms a rear power chamber. A port is provided in the hammer to permit intercommunication of the front and rear power chambers for the purpose of effecting the reciprocating motion of the hammer, said chambers being put in communication when the hammer is in the front portion of the cylindrical body.
The known ground perforating device under consideration operates by the action of compressed air supplied through the hose and sleeve into the front chamber. Forced by the air pressure, the hammer moves forward and, at the end of the stroke, strikes the front end of the cylindrical body. At this instant the compressed air passes from the rear chamber through the hammer port into the front chamber.
Inasmuch as the area of the hammer end face acted upon by the air pressure in the front chamber is larger than the area of the hammer end face acted upon the air pressure in the rear chamber, the force exerted on the hammer in the backward direction is greater than the force exerted thereon in the direction of forward travel. In consequence, the hammer moves backwards. When the hammer port becomes uncovered by the rear edge of the sleeve, the compressed air exhausts from the front chamber into the atmosphere. The air pressure in the front chamber drops below the air pressure in the rear chamber (which is equal to the supply pressure), the hammer is caused to move towards the front end of the cylindrical body, and the cycle commences over again.
For the ground perforating device to move in reverse, the sleeve is set in the rearmost position by rotating it by means of the air hose attached thereto.
With this setting of the sleeve, compressed air enters the rear chamber and periodically passes through the hammer port into the front chamber, thereby causing the hammer to reciprocate. However, in this case the hammer strikes the rear end of the cylindrical body and drives the perforating device back and out of the hole perforated by the forward motion.
The ground perforating device under consideration suffers from the disadvantage that in the case of a substantially long perforation it is difficult, if not impossible, to impart rotation to the sleeve through the air hose. Furthermore, the changeover from one direction of movement to the other takes too much time.
Also known in the art are ground perforating devices comprising a cylindrical body accommodating a hammer adapted to reciprocate therein. The rear end of the hammer is hollowed to accommodate a sleeve secured in the cylindrical body. The space between the outer walls of the hammer and the inner walls of the cylindrical body forms a front power chamber. The space between the walls of the hammer hollow and the end of the sleeve forms a rear power chamber. These chambers are interconnected by provision of a port in the hammer.
The sleeve has two circular projections between which are provided two longitudinal projections designed to limit axial movement of the sleeve and two recesses arranged to prevent the sleeve from rotation relative to the cylindrical body. The sleeve is installed in a hole in a guiding element which has two longitudinal grooves and a hole accommodating a spring-loaded retainer connected with a remote-control cable. The locking element of the retainer enters the sleeve recess for locking the sleeve in position. The longitudinal grooves are formed in the walls of the axial hole in the guiding element. The circular and longitudinal projections provide two locked positions of the sleeve, viz. one for forward movement and the other for reverse movement of the ground perforating device.
For the ground perforating device to move forward, the sleeve is positioned so that the hammer strikes the front end of the cylindrical body and practically at the same time compressed air is admitted into the front chamber. With this mode of operation, the hammer reciprocates, striking the front end of the cylindrical body.
To reverse the movement of the ground perforating device, the sleeve is to be set into the other extreme position. For the purpose the retainer remote-control cable is pulled by hand, whereby the locking element is disengaged from the recess in the sleeve. Thereafter, by rotating the air hose the sleeve is turned relative to the guiding element until the longitudinal projections on the sleeve are aligned with the grooves in the guiding element. By the action of the compressed air contained in the rear chamber the sleeve is moved away from the front end of the cylindrical body into the other position. To lock the sleeve in position, it is turned about the axis thereof by means of the air hose and thereafter the locking element is engaged by releasing the retainer remote-control cable.
With the sleeve in this position, the admission of compressed air into the front chamber is advanced and the exhaust of compressed air is retarded, as compared with the operation during the forward movement of the ground perforating device, whereby the hammer is caused to strike the rear end of the body, the ground perforating device moving in reverse.
The ground perforating device under discussion suffers from the disadvantage that the remote-control cable may become twisted with the air hose or caught on some object. Another disadvantage is that the turning of the air hose for effecting the reversal is difficult in case of long perforations. The aforementioned disadvantages hamper the operation of the ground perforating device in question.
Also known in the art is a ground perforating device comprising a cylindrical body accommodating a hammer adapted to reciprocate therein. The rear portion of the hammer has a hollow which accommodates a barrel secured in the cylindrical body. The space between the outer walls of the hammer and the inner walls of the cylindrical body forms a front power chamber. The space between the walls of the hammer hollow and the end of the barrel forms a rear power chamber. In order that reciprocating motion of the hammer may be effected, said chambers are interconnected by provision of a port in the hammer.
There is provided a sleeve, which sleeve is arranged to be turned relative to the barrel by provision of a shaped groove in the barrel into which fits a projection formed on the sleeve. The barrel has two rows of ports on the large-diameter portion thereof, whereas the sleeve has two rows of grooves on the large-diameter portion thereof, which grooves are arranged so that when the sleeve is turned relative to the barrel the sleeve walls cover one row of the barrel ports and uncover the other row. During forward movement of the ground perforating device the ports located nearer the front end of the cylindrical body are closed and the ports located nearer the rear end are open. Under these conditions compressed air enters the front chamber after the hammer ports have moved past the front edge of the barrel and the compressed air is exhausted through the open barrel ports.
When compressed air is supplied through the hose and the barrel into the rear chamber, the hammer moves toward the front end of the cylindrical body and, at the end of the forward stroke, strikes the body. At this instant compressed air passes from the rear chamber through the hammer ports into the front chamber. Due to the difference between the forces acting on the hammer from the front and rear chambers, the hammer is caused to move backwards. When the hammer ports have coincided with the barrel ports, the compressed air exhausts from the front chamber into the atmosphere.
The reversal of the ground perforating device is effected by shutting off the supply of compressed air. With the compressed air supply shut off, the sleeve is moved relative to the barrel by the action of a spring and is turned relative to the barrel by virtue of the shaped groove. Subsequently air to the ground perforating device is recommenced, the sleeve is turned some way further relative to the barrel, whereby the barrel ports nearer the front end of the cylindrical body are opened and the ports nearer the rear end are closed.
Under these conditions admission of compressed air into the front chamber is advanced and exhaust is retarded as compared with the forward mode of operation, owing to which the hammer strikes the rear end of the cylindrical body.
The ground perforating device under consideration suffers from the disadvantage that reversal is caused by any interruption of air supply, whether intentional or inadvertent, which is particularly inconvenient during the initial stage of perforation when compressed air supply is turned on and off over again for correcting the course of the perforating device.